The present invention relates to an optical waveguide circuit, which is used as a wavelength filter and an optical wavelength synthesizing and dividing device, etc., used for light transmissions, and a method for compensating the light transmission wavelength. In particular, the invention relates to an optical waveguide circuit which compensates for a fluctuation in temperature of the light transmission wavelength, and a method for compensating the light transmission wavelength thereof.
Recently, as a method to remarkably increase a transmission capacity in optical transmissions, studies and research have actively been carried out with respect to optical wavelength division multiplexing transmissions, and actual uses thereof have been commenced. The optical wavelength division multiplexing transmission is, for example, to transmit a plurality of lights having different wavelengths from each other while multiplexing the same. In such a system for optical wavelength division multiplexing transmission, it is indispensable to provide, in the system, an optical wavelength synthesizing and dividing device to pick up lights of each wavelength from the plurality of lights to be transmitted, at the light receiving side. Also, an optical wavelength synthesizing and dividing device used for optical wavelength division multiplexing transmissions is constructed so as to be provided with a light transmission device, which transmits only lights of predetermined wavelengths, or an optical reflection device, etc., which reflects only lights of predetermined wavelengths.
As one example of a light transmission device, there is a planar light waveguide circuit (PLC: Planar Light-wave Circuit) shown in, for example, FIG. 13. An optical waveguide circuit shown in the same drawing is called an arrayed waveguide diffraction grating (AWG: Arrayed Waveguide Grating). The arrayed waveguide diffraction grating 11 is such that a waveguide construction formed of a glass material is constructed on a substrate 1 formed of silicon, etc.,
In the waveguide construction, an input side slab waveguide 3 which acts as a first slab waveguide is connected to the emitting side of one or more optical input waveguides 2, and an array waveguide 40 which consists of a plurality of optical waveguides 4 is connected to the emitting side of the input side slab waveguide 3. An output side slab waveguide 5 which acts as the second slab waveguide is connected to the emitting side of the array waveguide 40 while a plurality of optical output waveguides 6 juxtaposed to each other are connected to the emitting side of the output side slab waveguide 5.
The array waveguide 40 propagates light emitted from the input side slab waveguide 3, which consists of optical waveguides 4 whose lengths are different from each other, wherein the lengths of optical waveguides adjacent to each other have a difference of xcex94L. Also, optical input waveguides 2 and optical output waveguides 6 are those that are provided, corresponding to the number of signal lights having wavelengths different from each other, which are divided by, for example, an arrayed waveguide diffraction grating 11. Further, the array waveguide 40 is formed of a number of optical waveguides 4, for example, 100 waveguides. However, in the same drawing, the number of respective optical waveguides 2, 4, and 6 are simplified and illustrated for simplification of the drawing.
For example, transmission side optical fibers (not illustrated) are connected to the optical input waveguides 2 to cause wavelength-multiplexed lights to be introduced. Lights introduced into the input side slab waveguide 3 through the optical input waveguides 2 are propagated by its diffraction effect and are made incident into the respective optical waveguides 4 of the array waveguide 40, whereby the lights are propagated in the respective optical waveguides 4 (array waveguide 40).
Lights propagated in the array waveguide 40 reach the output side slab waveguide 5, and are collected to and outputted to the optical output waveguides 6. Also, since the lengths of optical waveguides 4 which form the array waveguide 40 are different from each other, shifts arise in the phase of the individual light phase after the lights are propagated in the array waveguide 40. Accordingly, the wave plane of a convergent light is inclined in compliance with a shift amount of the phase, and a position, at which the convergent light is caused to converge, is determined by an angle of the inclination.
Further, where it is assumed that the angle (diffraction angle) is xcex8 at which a light is caused to converge when a light is made incident into the output side slab waveguide 5 from the array waveguide 40, there is a relationship between the xcex8 and the wavelength xcex of the convergent light as shown in the following expression.
nsxcex8+ncxcex94L=mxcexxe2x80x83xe2x80x83(1)
In expression (1), ns is a refractive index of the output side slab waveguide 5, and nc is a refractive index (effective refractive index) of optical waveguides 4 which forms an array waveguide 40. Also, m is the number of diffractions, whose figure is an integral number. In expression (1), where the wavelength is xcex when, for example, xcex8=0 is established, the following expression (2) can be established.
lxe2x80x940=ncxcex94L/mxe2x80x83xe2x80x83(2)
Therefore, the converging positions of lights having different wavelengths become different from each other, whereby it is possible to output lights having different wavelengths from different optical output waveguides 6 corresponding to the respective wavelengths.
An arrayed waveguide diffraction grating 11 has an optical dividing feature which, on the basis of the principle described above, divides lights having a plurality of wavelengths from those having the correspsonding plurality of wavelengths, different from each other, which are inputted from the optical input wavelengths 2, and outputs these from the respective optical output waveguides 6. And, a light transmission feature of the respective lights outputted from the respective optical output waveguides 6 becomes a feature as shown in, for example, FIG. 14(a). That is, the light transmission feature of the abovementioned respective lights has a light transmission feature in which the light transmission ratio is reduced in compliance with the wavelength being deviated from the center wavelength of the transmission of the respective lights centering around the center wavelengths of the respective light transmissions different from each other, in at least a predetermined wavelength area. In addition, the center wavelengths of the respective light transmissions in the light transmission feature are proportionate to a different (xcex94L) in the length of optical waveguides 4 forming an array waveguide 40, and effective refractive index nc of the optical waveguides 4.
In addition, the abovementioned light transmission feature does not necessarily have a relative maximum figure. For example, as shown in (b) in the same drawing, there may be a light transmission feature which has two relative maximum figures. Also, the wavelength showing the light transmission feature is not necessarily one for a specified optical output waveguide 6, and the wavelengths can be established, respectively, for the numbers m of diffraction which are different from each other in expression (1), wherein there exist a plurality of wavelengths for each of the numbers of diffraction. Therefore, where, for example, an arrayed waveguide diffraction grating is used for waveguide multiplexed light transmission, the number m of diffraction is determined so that the light transmission feature corresponds to the use wavelength of wavelength multiplexed optical transmission, whereby an arrayed waveguide diffraction grating 11 is designed.
Since the arrayed waveguide diffraction grating 11 has a feature as described above, it can be used as a wavelength multiplexing and dividing device for wavelength multiplexed transmission. For example, as shown in FIG. 13, as wavelength multiplexed lights having wavelengths xcex1, xcex2, xcex3, . . . xcexn (where n is an integral number exceeding 2) are inputted from one optical input waveguides 2, these lights are widened by input side slab waveguides 3 and reach the array waveguide 40. And, the lights reaching the array waveguide 40 pass through the array waveguide 40, further pass through the output side slab waveguide 5, and are caused to converge at positions different in compliance with wavelengths, and finally outputted from the emitting ends of optical output waveguides 6 through the respective optical output waveguides 6. The lights outputted from the optical output waveguides 6, that is, lights of the respective divided wavelengths are picked up via optical fibers (not illustrated) for output of lights, which are connected to the emitting ends of the respective optical output waveguides 6.
In this case, the transmission feature (wavelength feature of transmission light intensity of an array wavelength type diffraction grating 11) of lights outputted from the respective optical output waveguides 6 becomes as shown in FIG. 15 and becomes transmission spectra centering around the respective wavelengths (xcex1, xcex2, xcex3, . . . xcexn). Further, in the same drawing, wavelength features outputted from different optical output waveguides 6 are described in piles.
Also, since the arrayed waveguide diffraction grating 11 utilizes the principle of reversibility of an optical circuit, the same can be used as a wavelength multiplexing (synthesizing) device. That is, for example, as shown in FIG. 16, a plurality of lights having wavelengths different from each other are made, one by one, incident from the respective optical output wavelengths 6, these lights pass through the reversed propagation channel of the above channel, and synthesized by an array waveguide 40, and emitted from one optical input waveguide 2.
In such an array type waveguide diffraction grating 11, as described above, the diffraction grating is formed of an array waveguide 40, and a wavelength resolution power of the arrayed waveguide diffraction grating 11 is proportionate to difference (xcex94L) in length of the optical waveguides 4 forming the array waveguide 40. Therefore, by designing the xcex94L large, the arrayed waveguide diffraction grating 11 is capable of optically synthesizing wavelength multiplexed lights having a narrow interval which cannot be achieved by any of the prior arts. Accordingly, the arrayed waveguide diffraction grating 11 can accomplish an optical synthesizing and dividing feature (which is a feature by which a plurality of light signals whose wavelength interval is 1 nm or less) are divided or synthesized) necessary to achieve an optical wavelength multiplexing transmission of a higher-fiber packaging density. In addition, the arrayed waveguide diffraction grating 11 is, as described above, produced by accumulating and forming the waveguide configuration on a silicon substrate 1, using a glass material. The production is easy, which is preferable for mass production.
In order to use the arrayed waveguide diffraction grating 11 for wavelength multiplexing transmissions, it is necessary that the center wavelength of wavelengths which are divided or synthesized by an array waveguide 40, that is, the center wavelength of light transmission in the abovementioned light transmission feature is made coincident with a specified wavelength for wavelength multiplexed transmissions, so-called a grid wavelength. Also, as described above, the arrayed waveguide diffraction grating 11 is such a diffraction grating that divides multiplexed wavelengths and multiplexes wavelengths by utilizing a length of optical waveguides 4, which form the array waveguide 40, and a difference xcex94L in the length. Accordingly, in the arrayed waveguide diffraction grating 11, it is necessary to accurately form the difference xcex94L in the length of adjacent optical waveguides 4 forming an array waveguide 40.
Further, in order to use an array waveguide diffraction grating 11 for wavelength multiplexed optical transmissions, it is requested for the arrayed waveguide diffraction grating 11 that the center wavelength in the abovementioned light transmission is fixed in a use temperature range as a diffraction grating for wavelength multiplexed optical transmissions.
However, in an arrayed waveguide diffraction grating 11 produced in actuality, a shift arises in the length of optical waveguides 4 forming an array waveguide 40 due to a difference, etc., in production. Therefore, the center wavelength in the light transmissions in an arrayed waveguide diffraction grating 11 is not necessarily coincident with the abovementioned grid wavelength in a set temperature in the arrayed waveguide diffraction grating 11. Also, due to the following principle, since the center wavelength in the light transmissions in an arrayed waveguide diffraction grating 11 has a temperature dependency, the center wavelength may change in the abovementioned use temperature range.
That is, lengths of optical waveguides 4 forming an array waveguide 40 may change due to thermal expansion and thermal contraction of a substrate and/or optical waveguides 4, which are produced by a temperature change of the arrayed waveguide diffraction grating 11. In line therewith, a difference xcex94L in the length of the optical waveguides 4 may also change. Further, the effective refractive index nc of the optical waveguides 4 may change due to a temperature change of the arrayed waveguide diffraction grating 1. The length (optical path length or optical length) of an optical path of a light propagating in the array waveguide 40 may further change due to a temperature change of the arrayed waveguide diffraction grating 11. Therefore, since there is a change in the temperature of the arrayed waveguide diffraction grating 11, the collecting positions of lights condensed at the emitting end side of the output slab waveguide 5, passing through an array waveguide 40, may change. If so, the wavelengths of lights incident into the optical output waveguides 6 in the arrayed waveguide diffraction grating 11 shifts, whereby the center wavelength of the light transmission feature (the center wavelength of light transmissions) changes due to a temperature.
An amount of change in the center wavelength in light transmissions in line with the temperature changes can be obtained by differentiating the abovementioned expression (2) by using the temperature. The amount can be expressed by the following expression (3).
dxcex/dT=(xcex/nc)xc3x97(dnc/dT)+(xcex/L)xc3x97(dL/dT)xe2x80x83xe2x80x83(3)
In expression (3), the first term of the right side indicates temperature dependency of the effective refractive index of optical waveguides 4, and the second term of the right side indicates changes in temperature of the optical waveguides 4 forming an array waveguide 40 in line with expansion and contraction of a substrate 1.
FIG. 17 exemplarily shows the results of having measured transmission features of lights outputted from one optical output waveguide 6 in experiments, with respect to shifts in the center waveguide in the light transmission features. As shown in the same drawing, in the temperature range (a range from 0xc2x0 C. through 60xc2x0 C.) shown in the same drawing, the higher the temperature of an arrayed waveguide diffraction grating 11 becomes, the more the abovementioned center wavelength shifts to the longer wavelength side. Also, on the contrary, the lower the temperature of the arrayed waveguide diffraction grating 11 becomes, the more the center wavelength shifts to the shorter wavelength side.
It is considered that this is because an optical path sensed by lights passing through the array wavelength 40 is lengthened. It is considered that one of the reasons why the optical length sensed by lights passing through the array wavelength 40 is lengthened is that the first term of the right side of the abovementioned expression (3) is increased in line with an increase in the refractive index of glass being a waveguide material. Also, it is considered that another reason why the optical path sensed by lights passing through the array waveguide 40 is lengthened is that the length of the waveguide is physically increased by linear expansion of a substrate 1 and a waveguide material (that is, the second term of the right side of expression (3) is increased).
In addition, usually, a temperature regulating mechanism which can keep a waveguide circuit at a fixed temperature level is provided so that the center wavelength does not shift due to a temperature of the arrayed waveguide diffraction grating 11, whereby the temperature is kept at a fixed temperature level. That is, by providing such a temperature regulating mechanism, it is devised that no change arises in the refractive index and length of optical waveguides 4 which form an array waveguide 40.
The temperature regulating mechanism has a Peltier module 16 provided with a Peltier element, and a thermistor 18 as shown in, for example, FIG. 18. These elements are connected to a temperature controller (not illustrated) by a conductor 17. Also, the thermistor 18 is attached to a temperature holding plate 12 which intervenes between the Peltier module 16 and the substrate 1. Usually, a thermal silicone oil compound and a thermal silicone RTV (Room temperature vulcanizing agent) are provided between the substrate 1 and the temperature holding plate 12, and between the temperature holding plate 12 and the Peltier module 16, so that the heat transmission can be improved.
In an arrayed waveguide diffraction grating 11 in which such a temperature control mechanism is provided, the temperature of the temperature holding mechanism 12 is detected by the thermistor 18, and an electric current flowing in the Peltier module 16 is controlled while feeding back the figure by a temperature controller. If so, the temperature is accurately controlled so that the temperature of the arrayed waveguide diffraction grating 11 is fixed.
In order to make the center waveguide of transmission of the respective lights in the light transmission feature of the respective light outputted from the optical output waveguide 6 of the arrayed waveguide diffraction grating 11 coincident with the grid waveguide, the following control may be carried out. That is, a temperature at which the center wavelength of the light transmission is made coincident with the grid wavelength is established as the setting temperature, wherein the arrayed waveguide diffraction grating 11 may be used while the diffraction grating 11 is kept at the set temperature by the temperature holding mechanism. Also, it is considered that a temperature holding mechanism provided with a heater instead of the Peltier module 16 may be made available.
However, in order to keep the temperature of the arrayed waveguide diffraction grating 11 at a fixed level by providing such a temperature holding mechanism, it is necessary to prepare a heat generating or heat absorbing body such as a Peltier module 16 or a heater, a temperature detecting device such as a thermistor 18, and a temperature controller to control these elements, a power source, etc. Accordingly, an arrayed waveguide diffraction grating module in which these elements are provided becomes very expensive in cost, and further the module size thereof is also increased. That is, such shortcomings or problems arise.
Further, a Peltier module 16, a thermistor 18, a temperature controller, etc., are electrical components. If any difference in temperature occurs due to differences in these components, a shift may arise in compensation of the center waveguide of transmission of the lights, which is held by the temperature control of these elements. Therefore, control for which the temperature holding mechanism is provided has less reliability in compensation of the center wavelength of transmission of lights.
On the other hand, recently, an arrayed waveguide diffraction grating 11 of such a type as shown in FIG. 19 has been proposed. In the proposal, a groove 13 crossing an array waveguide 40 is formed on the path of the array waveguide 40, and a silicone resin 14, etc., whose refractive index is different from that of the array waveguide 40 is filled up in the groove, a shift in the center wavelength resulting from changes in the temperature can be compensated. The silicone resin 14 has a negative refractive temperature coefficient. Therefore, the groove 13 is made triangular in its cross section, and the length of silicone resin 14 filled therein is lengthened in line with an increase in the length of optical waveguides 4 forming the array waveguide 40. Thereby, all the wavelengths divided or synthesized by the array waveguide 40 are compensated by the silicone resin 14 with respect to the temperature, whereby the center wavelength of transmission of the lights can be compensated.
However, since an arrayed waveguide diffraction grating 11 of such a type is to compensate the temperature of the center wavelength of light transmission by a silicone resin 14 secured in the groove 13, it is necessary that the groove 13 be very accurately formed. Accordingly, it is very difficult to produce the arrayed waveguide diffraction grating 11, and mass production thereof is also difficult, whereby the cost of such an arrayed waveguide diffraction grating 11 is increased.
Further, in such an arrayed waveguide diffraction grating 11, even though the waveguide of the arrayed waveguide diffraction grating 11 and the groove 13 are accurately formed, it is unavoidable that a difference in production occurs. Therefore, where the center wavelength of the light transmission shifts from the grid wavelength due to the difference in production, the center length of the light transmission cannot be made coincident with the grid wavelength. Accordingly, when the center wavelength of the light transmission shifts from the grid wavelength in the construction illustrated in FIG. 13, it is necessary, as in FIG. 18, to construct the array waveguide type diffracting grating 11 by providing a Peltier module 16, etc., whereby the production cost is further increased.
In addition, where the arrayed waveguide diffraction grating 11 is used in, for example, an atmosphere whose temperature is kept at a predetermined temperature level, a shift in the center wavelength of the light transmission is compensated by the following method. That is, where the center wavelength shifts from the grid wavelength due to a difference in production of an arrayed waveguide diffraction grating 11, an intensive ultraviolet ray is irradiated onto an array waveguide 40, whereby since the refractive index of the array waveguide 40 permanently changes, it becomes possible to compensate the shift of the center wavelength of the light transmission. However, in the case of using this method, it is difficult to control the irradiation intensity and time of an ultraviolet ray, and the ultraviolet ray irradiation apparatus is large-sized and becomes expensive.
The present invention was developed to solve the abovementioned shortcomings and problems as in the prior arts, and it is therefore an object of the invention to provide an optical waveguide circuit which does not need any large-sized apparatus, is capable of compensating a temperature dependency of the center wavelength of light transmissions of an optical waveguide circuit such as an arrayed waveguide diffraction grating, and a shift from a predetermined set wavelength with ease and at a low cost, and a method for compensating the light transmission wavelengths.
In order to achieve the above object, the invention is provided with the means constructed as described above, in order to solve the abovementioned shortcomings and problems. That is, an optical waveguide circuit according to a first aspect of the invention, in which a first slab waveguide is connected to the emitting side of one of more optical waveguides juxtaposed to each other, an array waveguide, consisting of a plurality of waveguides whose lengths are different from each other, which propagates lights led out from the correspsonding first slab waveguide is connected to the emitting side of the corresponding first slab waveguide, a second slab waveguide is connected to the emitting side of the corresponding array waveguide, a waveguide construction, consisting of a plurality of optical output waveguides juxtaposed to each other, is formed on a substrate at the emitting side of the corresponding second slab waveguide, having an optical dividing feature for dividing lights of a plurality of wavelengths from lights having a plurality of wavelengths different from each other, which are inputted from the corresponding optical input waveguides, and outputting the same from respective optical output waveguides, light transmission features of the respective lights outputted from the respective corresponding optical output waveguides having the center wavelengths of light transmission different from each other in at least a predetermined wavelength area, and compensating a temperature dependency fluctuation of the center wavelengths of the light transmission; wherein by providing the corresponding array waveguide or the corresponding array waveguide and the first and second slab waveguides with a stress applying means for applying a stress dependent on a temperature in the direction of reducing the temperature dependency fluctuation of the center wavelengths of the corresponding respective light transmissions, the temperature dependency fluctuation of the center wavelengths of the corresponding respective light transmissions is reduced.
Further, an optical waveguide circuit according to a second aspect of the invention is featured in that, in addition to the first aspect of the invention, the temperature dependency fluctuation of the center wavelengths of the respective light transmissions in a temperature range from 0xc2x0 C. through 70xc2x0 C. is reduced to 0.3 nm or less.
In addition, an optical waveguide circuit according to a third aspect of the invention is featured in that, in addition to the first aspect of the invention, a reference temperature is measured, at which the center wavelengths of the corresponding respective light transmissions becomes a predetermined wavelength, a stress applying means is provided, in which a stress applied to the array waveguide or the corresponding array waveguide, and the first and second slab waveguides becomes zero, and the absolute figure of the stress is increased in line with an actual temperature shifting from the corresponding reference temperature, and the corresponding stress applying means is provided in the optical waveguide circuit in an atmosphere of the corresponding reference temperature, wherein a shift amount of the center wavelengths of the corresponding respective light transmissions from the corresponding set wavelength is kept within a shift amount predetermined in a predetermined temperature range including at least the corresponding reference temperature.
Further, an optical waveguide circuit according to a fourth aspect of the invention is featured in that, in addition to the first aspect of the invention, a reference temperature is measured, at which the center wavelengths of the corresponding respective light transmissions becomes a predetermined wavelength, a stress applying means is provided, in which a stress applied to the array waveguide or the corresponding array waveguide, and the first and second slab waveguides becomes zero, and the absolute figure of the stress is increased in line with an actual temperature shifting from the corresponding reference temperature, and the corresponding stress applying means is provided in the optical waveguide circuit in an atmosphere of the corresponding reference temperature, wherein the center wavelengths of the corresponding respective light transmissions are made into almost the corresponding set wavelengths in a predetermined temperature range including at least the corresponding reference temperature.
Also, an optical waveguide circuit according to a fifth aspect of the invention is featured in that, in addition to the first aspect of the invention, a stress applying means is provided, which applies a stress to an array waveguide or the corresponding array waveguide and the first and second slab waveguides in the corresponding set temperature so that the center wavelengths of the corresponding respective light transmissions become set wavelengths predetermined in a predetermined set temperature, and the corresponding stress applying means is provided in the correspsonding optical waveguide circuit at an atmosphere temperature where the stress applied from the corresponding array waveguide or the corresponding array waveguide, and the first and second slab waveguides become zero, wherein the center wavelengths of the corresponding respective light transmissions are made into almost the corresponding set wavelengths in the corresponding set temperature.
In addition, an optical waveguide circuit according to a sixth preferred embodiment of the invention, in which a first slab waveguide is connected to the emitting side of one of more optical waveguides juxtaposed to each other, an array waveguide, consisting of a plurality of waveguides whose lengths are different from each other, which propagate lights led out from the corresponding first slab is connected to the emitting side of the corresponding first slab waveguide, a second slab waveguide is connected to the emitting side of the corresponding array waveguide, a waveguide construction, consisting of a plurality of optical output waveguides juxtaposed to each other, is formed on a substrate at the emitting side of the corresponding second slab waveguide, having an optical dividing feature for dividing lights of a plurality of wavelengths from lights having a plurality of wavelengths different from each other, which are inputted from the corresponding optical input waveguides, and outputting the same from respective optical output waveguides, light transmission features of the respective lights outputted from the respective corresponding optical output waveguides having the center wavelengths of light transmission different from each other in at least a predetermined wavelength area, and compensating a temperature dependency fluctuation of the center wavelengths of the light transmission; wherein, when the center wavelengths of the corresponding light transmissions, respectively, shifts by an almost equal shift amount of wavelength from the respective predetermined wavelengths corresponding to the center wavelengths of the respective light transmissions, a shift of the center wavelengths of the corresponding respective light transmissions is reduced by providing a stress applying means which applies a stress in the direction of reducing the corresponding shift amount of wavelength to the corresponding array waveguide, and the corresponding array waveguide, and the first and second slab waveguides.
Also, an optical waveguide circuit according to a seventh aspect of the invention is featured in that, in addition to any one of the first through sixth aspect of the invention, a warp applying means which applies a stress to an optical waveguide by warping the corresponding substrate is provided as a stress applying means.
In addition, an optical waveguide circuit according to an eighth aspect of the invention is featured in that, in addition to any one of the first through sixth aspect of the invention, a pressure applying means which applies pressure to the corresponding substrate in the vertical direction is provided as a stress applying means.
Further, an optical waveguide circuit according to a ninth aspect of the invention is featured in that, in any one of the first through sixth aspect of the invention, a horizontal direction stress applying means which applies a tensile force or a compression force to the corresponding substrate in the horizontal direction is provided as a stress applying means.
Also, an optical waveguide circuit according to a tenth aspect of the invention is featured in that, in addition to the seventh aspect of the invention, a warp applying portion whose linear expansion coefficient is different from that of the corresponding substrate is provided with at least one of either the surface side of the corresponding optical waveguide or the rear side of the substrate to form a warp applying means.
In addition, an optical waveguide circuit according to an eleventh aspect of the invention is featured in that, in addition to the tenth aspect of the invention, a resin layer or a filler-contained resin layer is formed with at least one of either the surface side of the corresponding optical waveguide or the rear side of the substrate as a warp applying portion.
Further, an optical waveguide circuit according to a twelfth aspect of the invention is featured in that, in addition to the seventh aspect of the invention, a plate-shaped member whose linear expansion coefficient is different from that of the corresponding substrate is adhered to or welded to at least one of either the surface side of the optical waveguide or the rear side of the substrate to form a warp applying means.
Still further, an optical waveguide circuit according to a thirteenth aspect of the invention is featured in that, in addition to the seventh aspect of the invention, a temperature dependent warp changing portion in which the warp amount is changed on the basis of a temperature is provided with at least one of either the surface side of the optical waveguide or the rear side of the substrate to form a warp applying means.
And, an optical waveguide circuit according to a fourteenth aspect of the invention is featured in that, in addition to the thirteenth aspect of the invention, a plurality of plates whose linear expansion coefficients are different from each other are bonded to form a temperature dependent warp changing portion.
Further, an optical waveguide circuit according to a fifteenth aspect of the invention is featured in that, in addition to the thirteenth aspect of the invention, a temperature dependent warp changing portion is formed of a shape memory alloy plate.
Still further, a method (method for compensating a light transmission wavelength of an optical waveguide circuit) according to a first aspect of the invention, in which a first slab waveguide is connected to the emitting side of one of more optical waveguides juxtaposed to each other, an array waveguide, consisting of a plurality of waveguides whose lengths are different from each other, which propagate lights led out from the corresponding first slab is connected to the emitting side of the corresponding first slab waveguide, a second slab waveguide is connected to the emitting side of the corresponding array waveguide, a waveguide construction, consisting of a plurality of optical output waveguides juxtaposed to each other, is formed on a substrate at the emitting side of the corresponding second slab waveguide, having an optical dividing feature for dividing lights of a plurality of wavelengths from lights having a plurality of wavelengths different from each other, which are inputted from the corresponding optical input waveguides, and outputting the same from respective optical output waveguides, light transmission features of the respective lights outputted from the respective corresponding optical output waveguides having the center wavelengths of light transmission different from each other in at least a predetermined wavelength area, and compensating a temperature dependency fluctuation of the center wavelengths of the light transmission; wherein by providing the corresponding array waveguide or the corresponding array waveguide and the first and second slab waveguides with a stress applying means for applying a stress dependent on a temperature in the direction of reducing the temperature dependency fluctuation of the center wavelengths of the corresponding respective light transmissions, the temperature dependency fluctuation of the center wavelengths of the corresponding respective light transmissions is reduced.
A method according to a second aspect of the invention is featured in that, in addition to the first aspect of the invention, the temperature dependency fluctuation of the center wavelengths of the respective light transmissions in a temperature range from 0xc2x0 C. through 70xc2x0 C. is reduced to 0.3 nm or less.
In addition, a method according to a third aspect of the invention is featured in that, in addition to the first aspect of the invention, a reference temperature is measured, at which the center wavelengths of the corresponding respective light transmissions become a predetermined wavelength, a stress applying means is provided, in which a stress applied to the array waveguide or the corresponding array waveguide, and the first and second slab waveguides becomes zero, and the absolute figure of the stress is increased in line with an actual temperature shifting from the corresponding reference temperature, and the corresponding stress applying means is provided in the optical waveguide circuit in an atmosphere of the corresponding reference temperature, wherein a shift amount of the center wavelengths of the corresponding respective light transmissions from the corresponding set wavelength is kept within a shift amount predetermined in a predetermined temperature range including at least the corresponding reference temperature.
Further, a method according to a fourth aspect of the invention is featured in that, in addition to the first aspect of the invention, a reference temperature is measured, at which the center wavelengths of the corresponding respective light transmissions become a predetermined wavelength, a stress applying means is provided, in which a stress applied to the array waveguide or the corresponding array waveguide, and the first and second slab waveguides becomes zero, and the absolute figure of the stress is increased in line with an actual temperature shift from the corresponding reference temperature, and the corresponding stress applying means is provided in the optical waveguide circuit in an atmosphere of the corresponding reference temperature, wherein the center wavelengths of the corresponding respective light transmissions are made into almost the corresponding set wavelengths in a predetermined temperature range including at least the corresponding reference temperature.
Also, a method according to a fifth aspect of the invention is featured in that, in addition to the first aspect of the invention, a stress applying means is provided, which applies a stress to an array waveguide or the corresponding array waveguide and the first and second slab waveguides in the corresponding set temperature so that the center wavelengths of the corresponding respective light transmissions become set wavelengths predetermined in a predetermined set temperature, and the corresponding stress applying means is provided in the correspsonding optical waveguide circuit at an atmosphere temperature where the stress applied from the corresponding array waveguide or the corresponding array waveguide, and the first and second slab waveguides become zero, wherein the center wavelengths of the corresponding respective light transmissions are made into almost the corresponding set wavelengths in the corresponding set temperature.
In addition, a method according to a sixth preferred embodiment of the invention, in which a first slab waveguide is connected to the emitting side of one of more optical waveguides juxtaposed to each other, an array waveguide, consisting of a plurality of waveguides whose lengths are different from each other, which propagate lights led out from the corresponding first slab is connected to the emitting side of the corresponding first slab waveguide, a second slab waveguide is connected to the emitting side of the corresponding array waveguide, a waveguide construction, consisting of a plurality of optical output waveguides juxtaposed to each other, is formed on a substrate at the emitting side of the corresponding second slab waveguide, having an optical dividing feature for dividing lights of a plurality of wavelengths from lights having a plurality of wavelengths different from each other, which are inputted from the corresponding optical input waveguides, and outputting the same from respective optical output waveguides, light transmission features of the respective lights outputted from the respective corresponding optical output waveguides having the center wavelengths of light transmission different from each other in at least a predetermined wavelength area, and compensating a temperature dependency fluctuation of the center wavelengths of the light transmission; wherein, when the center wavelengths of the corresponding light transmissions, respectively, shifts by an almost equal shift amount of wavelength from the respective predetermined wavelengths corresponding to the center wavelengths of the respective light transmissions, a shift of the center wavelengths of the corresponding respective light transmissions is reduced by providing a stress applying means which applies a stress in the direction of reducing the corresponding shift amount of wavelength to the corresponding array waveguide, and the corresponding array waveguide, and the first and second slab waveguides.
Also, a method according to a seventh aspect of the invention is featured in that, in addition to any one of the first through sixth aspect of the invention, a warp applying means which applies a stress to an optical waveguide by warping the corresponding substrate is provided as a stress applying means.
In addition, a method according to an eighth aspect of the invention is featured in that, in addition to any one of the first through sixth aspect of the invention, a pressure applying means which applies pressure to the corresponding substrate in the vertical direction is provided as a stress applying means.
In addition, a method according to an eighth aspect of the invention is featured in that, in addition to any one of the first through sixth aspect of the invention, a pressure applying means which applies pressure to the corresponding substrate in the vertical direction is provided as a stress applying means.
Further, a method according to a ninth aspect of the invention is featured in that, in any one of the first through sixth aspect of the invention, a horizontal direction stress applying means which applies a tensile force or a compression force to the corresponding substrate in the horizontal direction is provided as a stress applying means.
Also, a method according to a tenth aspect of the invention is featured in that, in addition to the seventh aspect of the invention, a warp applying portion whose linear expansion coefficient is different from that of the corresponding substrate is provided with at least one of either the surface side of the corresponding optical waveguide or the rear side of the substrate to form a warp applying means.
In addition, a method according to an eleventh aspect of the invention is featured in that, in addition to the tenth aspect of the invention, a resin layer or a filler-contained resin layer is formed with at least one of either the surface side of the corresponding optical waveguide or the rear side of the substrate as a warp applying portion.
Further, a method according to a twelfth aspect of the invention is featured in that, in addition to the seventh aspect of the invention, a plate-shaped member whose linear expansion coefficient is different from that of the corresponding substrate is adhered to or welded to at least one of either the surface side of the optical waveguide or the rear side of the substrate to form a warp applying means.
Still further, a method according to a thirteenth aspect of the invention is featured in that, in addition to the seventh aspect of the invention, a temperature dependent warp changing portion in which the warp amount is changed on the basis of a temperature is provided with at least one of either the surface side of the optical waveguide or the rear side of the substrate to form a warp applying means.
And, a method according to a fourteenth aspect of the invention is featured in that, in addition to the thirteenth aspect of the invention, a plurality of plates whose linear expansion coefficients are different from each other are bonded to form a temperature dependent warp changing portion.
Further, a method according to a fifteenth aspect of the invention is featured in that, in addition to the thirteenth aspect of the invention, a temperature dependent warp changing portion is formed of a shape memory alloy plate.
The first through the fifth aspects of the invention are such that a stress applying means which applies a stress dependent on a temperature in the direction of reducing the temperature dependency fluctuations of the center wavelengths of transmissions of the respective lights outputted from the respective optical output waveguides of an optical waveguide circuit is provided in an array waveguide or the corresponding array waveguide and the first and second slab waveguides. That is, the first through the fifth aspects of the invention can reduce the temperature dependency fluctuations of the center wavelengths of the corresponding light transmissions with ease and with high reliability, and can reduce the temperature fluctuation of the respective light transmission wavelengths.
In particular, according to the second aspect of the invention, since the temperature dependency fluctuation of the center wavelength of the respective light transmissions in a temperature range from 0xc2x0 C. through 70xc2x0 C. can be reduced to 0.3 nm or less, the temperature dependency fluctuation of the center wavelength of the respective light transmissions in a temperature range from 10xc2x0 C. through 50xc2x0 C. can be reduced to 0.3 nm or less, whereby when an optical waveguide circuit is used for wavelength multiplexed optical transmissions indoors, it is possible to use the optical waveguide circuit without any difficulty. Also, according to the second aspect, by reducing the temperature dependency fluctuations of the center wavelength of the respective light transmissions in a temperature range from 0xc2x0 C. through 70xc2x0 C. to 0.3 nm or less, it becomes possible to reduce the temperature dependency fluctuations of the center wavelengths of the corresponding respective light transmissions in the current usage temperature range for wavelength-multiplexed transmissions to a very small figure. Therefore, with the second aspect, it is possible to use the optical waveguide circuit for wavelength-multiplexed transmissions not only indoors but also outdoors without any difficulty, and it is possible to form an optical waveguide circuit best suited to wavelength multiplexed transmissions.
Still further, the third aspect of the invention is such that a stress applying means is provided in an optical waveguide circuit in an atmosphere of the reference temperature, wherein the stress applied to the array waveguide or the corresponding array waveguide, and the first and second slab waveguides in the reference temperature at which the center wavelengths of the corresponding respective light transmission become a predetermined set wavelength become zero, and the stress applying means increase the absolute value of the stress in line with shifts of a temperature from the corresponding reference temperature. Therefore, in the third aspect of the invention, by providing the stress applying means, it is possible to keep the shift amount of the center wavelengths of the corresponding respective light transmissions from the corresponding set wavelength within a predetermined set shift amount in a predetermined set temperature range including at least the reference temperature. Therefore, the third aspect of the invention can further make an optical waveguide circuit into an excellent optical waveguide circuit suitable for wavelength multiplexed optical transmissions.
In addition, the fourth aspect of the invention provides a stress applying means similar to that of the third aspect of the invention, wherein the corresponding stress applying means is employed in an atmosphere of the corresponding reference temperature, whereby in the fourth aspect of the invention, the center wavelength of the corresponding respective light transmission can be made into almost the set wavelength in a predetermined temperature range including at least the reference temperature. Therefore, the fourth aspect of the invention can eliminate almost all of not only the temperature dependency of the center wavelength of the corresponding light transmission but also a shift of the center wavelength of light transmission from the set wavelength such as the grid wavelength, etc., whereby an optical waveguide circuit can be further made into an excellent waveguide circuit suitable for a wavelength multiplexed optical transmission.
Also, in the fifth aspect of the invention, first, a stress applying means is provided, which applies a stress to an array waveguide, or the corresponding array waveguide, and the first and second slab waveguides at a predetermined set temperature so that the center wavelength of the respective light transmission is made into a predetermined set wavelength at the corresponding predetermined temperature. And, the stress applying means is provided in an optical waveguide circuit in an atmosphere of a temperature where the stress applied from the corresponding stress applying means to the array waveguide or the corresponding array waveguide, and the first and second slab waveguides become zero. Thereby, the fifth aspect of the present invention ensures that the center wavelength of the corresponding respective light transmission is made into almost the set wavelength at the corresponding set temperature. Therefore, if, in the fifth aspect of the invention, the use temperature in which the optical waveguide circuit is used for, for example, a wavelength multiplexed optical transmission, is determined at the corresponding set temperature, an optical waveguide circuit according to the fifth aspect of the invention can be made into an excellent optical waveguide circuit in which almost no shift from the set wavelength of the center wavelength of the respective light transmission at the corresponding set temperature is produced. Accordingly, in compliance with the fifth aspect of the invention, it is possible to make the optical waveguide circuit into an optical waveguide circuit best suited to a wavelength multiplexed optical transmission, etc.
Still further, the sixth aspect of the invention is such that, when the center wavelength of the respective light transmission shifts by wavelengths equal to each other from the respective predetermined wavelengths corresponding thereto, a stress applying means is provided, which applies a stress in the direction of diminishing the corresponding shift amount of wavelength to the array waveguide, or the corresponding array waveguide, and the first and second slab waveguides. And, by providing the stress applying means, it is possible to diminish a shift of the center wavelength of the respective light transmission. For this reason, according to the sixth aspect of the present invention, it is possible to very easily compensate a shift of the grid wavelength of the center wavelength of light transmission of an optical waveguide circuit such as an arrayed waveguide diffraction grating from the set wavelength at high reliability.
Also, according to a construction in which a warp applying means which applies a stress to an optical waveguide by warping the reference plane is provided as the stress applying means, a stress is applied onto the optical waveguide by warping the reference plane by warping the warp applying means, whereby the abovementioned excellent effect can be easily brought about.
In addition, according to a construction in which a pressure applying means for applying pressure in the direction vertical to the reference plane is provided as a stress applying means, a stress is applied to an optical waveguide by applying pressure in the direction vertical to the reference plane by the pressure applying means, whereby the abovementioned excellent effect can be easily brought about.
According to a construction in which a horizontal direction stress applying means which applies a tensile force or a compression force to the reference plane in the horizontal direction is provided as the stress applying means, a stress can be applied to an optical waveguide by applying a tensile force or a compression force to the reference plane in the horizontal direction by the horizontal direction stress applying means. With this construction, the abovementioned excellent effect can be easily brought about.
Also, according to a construction in which a warp applying portion whose linear expansion coefficient is different from that of the substrate is provided at least one of either the surface side of an optical waveguide or the rear side of the substrate in order to form a warp applying means, the warp applying means can be easily formed, and the abovementioned excellent effect can be brought about.
In addition, according to a construction in which a resin layer or filler-contained resin layer is formed at least one of either the surface side of an optical waveguide or the rear side of the substrate to bring about a warp applying portion, it is possible to easily form a warp applying portion, whereby the abovementioned effect can be brought about.
Further, according to a construction in which a plate-shaped member whose linear expansion coefficient is different from that of the substrate is adhered to or welded to at least one side of the surface side of an optical waveguide and the rear side of the substrate to form a warp applying means, the warp applying means can be very easily formed, and the abovementioned effect can be brought about. Still further, according to a construction in which a temperature dependency warp changing portion which changes the warping amount depending on a temperature is provided at least one of either the surface side of an optical waveguide or the rear side of the substrate to form a warp applying means, the warp applying means can be very easily formed, whereby the abovementioned excellent effect can be displayed.
Also, according to a construction in which a temperature dependency warp changing portion is formed by bonding a plurality of plates whose linear expansion coefficients are different from each other or a construction in which a temperature dependency warp changing portion is formed by using a shape memory alloy plate, the temperature dependency warp changing portion can be very easily formed, and the abovementioned excellent effect can be displayed.
Therefore, in the present invention, in either constructions described above, a stress applying means can be easily formed as described above, whereby a stress can be applied to an array waveguide or the corresponding array waveguide, and the first and second slab waveguides. Therefore, the invention does not require any large-sized apparatus, and is capable of compensating a shift of the center wavelength of the respective light transmission from the temperature dependency and established wavelengths with ease and at low cost.